Add .eval when exporting flac

[yygle]

@lucidrains Thanks for the awesome work. You may forgot to add .eval() when exporting the flac files in soundstream trainer. And it may cause differences for the output wavs.

[lucidrains]

@yygle oh, wasn't that done here? or are you referring to somewhere else?

[yygle]

sorry, my mistake. It use different names, self.soundstream and self.model.

[lucidrains]

@yygle yea, there is an EMA version

no worries, thanks for raising the issue!